Preventing darkening and formation of precipitates in solutions of photographic developers



United States Patent 6 Claims. (or. 96-29) This invention relates to compounds being capable of preventing darkening and the formation of precipitates in solutions of photographic developers. It is known that used solutions of developers darken and that in those developers metallic silver precipitates. This is particularly the case in fixing developers and in developers for the silver salt dilfusion process, because in these special processes silver halide is dissolved out from unexposed and undeveloped material to be treated. The silver compounds which are dissolved are generally not stable in the developer solutions and are reduced, forming metallic silver.

This precipitation of silver produces stains because the silver gets deposited on the photographic materials.

When the silver salt diffusion process is carried out in developing apparatus which are known for this purpose, mud consisting of metallic silver is deposited on the guide elements if the developer remains unused for some time and is left in the apparatus. When the developer is used again, this muddy deposit is taken up by the material carried through the developer, producing stains on the positives, which are generally not Washed.

In order to avoid any confusion it will be convenient here to point out that those compounds which conventionally are added to the developer solution as antifog agents for preventing the formation of fog in the silver halide emulsion layer being developed have nothing to do with the compounds according to the invention because these keep clear the developer solution only and have no influence at all on the photographic materials being processed in said solution.

It is among the objects of the invention to provide novel products for keeping clear photographic developer solutions in particular developer solution for the silver salt diffusion process, thus providing developer compositions having improved chemical and photographic properties.

It has now been found that darkening of the developer and formation of a black silver mud can be avoided by adding to the developer solution derivatives of Z-mercapto- 1,3,4-thiadiazoles of the general formulae:

H's-( i l-X131 HS-(J -X-Jiz-X-i] i l-SH (III) NN NN Hsii-(oEnn-ii ("l-SH s s wherein X is a bivalent radical such as the S (thio) or =NH (imino),

R represents a radical such as alkyl with 3-16 carbon atoms cycloalkyl, aryl or aralkyl which in turn may be "ice The following compounds are very useful for the instant purpose:

General Formula I:

II II B. 8-0 CXR S Melting No. --X-R1 represents -SR po int in R1=n-butyl 97-98 R1=n-pe11tyl 67-68 R n-hexyl- 70-71 R =n-o ctyl 78-79 R1=n-decyl 84-86 R1= n-dodecyl 86-87 R1=n-tetradecyl 90-91 R n hexadeeyl 91-92 R1=isopropyl 118-119 R1=isobutyl 97-98 R1 =B-phenylethy 103 R =benzyl 129 R =4-n1ethylbenzyl 144 R =2,4-dimethylbenzyl, R1= 4-chlorobenzyl 156 R =cyclohexyl 157 XR1 represents -NHR I R =n-butyl 133-134 R1=n-hexyl 96-98. 5 R1=n-octyl 89-91 R =n-dodecyl 87-88 R1= cyelohexylm 184 R1 4-methylcyclohexyl 156-158 R1=benzy1 139. 5-140 R1=phenyl 206 R =4-diphenylene 283 R 4-methylphenylen 218-219 R1 4-methoxyphenylene 186-187 R 4-cyclohexylphenyleue- 175-177 R; =B-phenylethyl 152-153. 5

General Formula II:

6*? F? HSC C-XRz-XC C-SH Melting No. X represents S- P9313; in

30 R2 butylene 191-193 R hexylene. 162-163 R octylene. -147 R; deeylene 181-132 34 Rz=CHrCHz-. 223

35 -CH CH3 220 -X represents NH- 134 194-197 z=- H2) s 198-199 39 R =1,4-cyclohexylene 271-273 are dissolved in 350 cm? dimethylformamide.

The compound of the general Formula I can be prepared without difliculties according to one of the following methods: e.g. compounds 1-16 by reacting 2,5-dimercaptothiadiazole with halogen-substituted alkanes in the presence of alkali-metal hydroxide.

COMPOUND 3 3 g. (0.2 mol) of 2,5-dirnercapto-1,3,4-thiadiazole are dissolved in 240 cm. of 80% aqueous ethanol containing 8 g. (0.2 mol) sodium hydroxide. After adding 33 g. (0.2 mol) of l-bromohexane the reaction mixture is refluxed for 12 hours and thereafter concentrated by evapo- COMPOUND This compound is prepared according to the method described herein for the preparation of compound 3 with the exception that 27.4 g. of 2-chlorobutane are added and the reaction mixture is refluxed for 13 hours.

Yield: 14.5 g. Melting point: 9798.

COMPOUND 12 30 g. (0.2 mol) of 2,5-dimercapto-1,3,4-thiadiazole are dissolved in 240 cm. of 80% aqueous ethanol containing 8 g. (0.2 mol) sodium hydroxide. After adding 25.3 g. (0.2 mol) of benzyl chloride the reaction mixture is refluxed for 2 hours. The product which precipitates after cooling is filtered by suction and washed with water until free from halogen. For purification the raw product is dissolved in dilute aqueous potassium hydroxide and reprecipitated with dilute hydrochloric acid.

Yield: 16.5. g. Melting point: 9798.

Compounds 17-29 may be produced by reacting substituted thiosemicarbazide with carbondisulphide according to the following method:

COMPOUND 21 43.3 g. (0.25 mol) of 4-cyclohexylthiosemicarbazide 35 cm. of carbon disulphide are added dropwise to this solution with stirring at room temperature. The reaction mixture is then heated for 90 minutes to 65 C. and stirred at this temperature until the evolution of hydrogen sulphide is completed. The product is precipitated by stirring into ice-cooled hydrochloric acid. The precipitated product is separated by suction filtration and washed with water until free from halogen. The crude product is purified by reprecipitation.

Yield: 41 g. Melting point: 184-185".

COMPOUND 24 This compound was prepared in accordance with the method described by Martin Freund and Hans Imgart in Berichte der deutschen chemischen Gesellschaft, vol. 28, pages 946957 (1895).

The compounds of the general Formula II may be prepared according to one of the following methods: e.g. compounds 30-35 by reacting 2,5-dimercapto-1,3,4-thiadiazole with a,w-dihalogen-alkanes in alcoholic solution in the presence of alkali hydroxide; compounds 3641 according to the method described herein for the preparation of compound 21.

COMPOUND 31 30 g. (0.2 mol) 2,5-dimercapto-1,3,4-thiadiazole are dissolved in 240 cm. of aqueous ethanol containing 8 g. (0.2 mol) of sodium hydroxide. After adding 24.4 g. (0.1 mol) of 1,6-dibromohexane it is refluxed for one hour. Thereafter it is cooled and the precipitate suction filtered and washed with Water until free from halogen. The raw product is dissolved in dilute potassium hydroxide and reprecipitated by adding dilute hydrochloric acid.

Yield: 28 g. Melting point: 162163.

COMPOUND 34 30 g. (0.2 mol) 2,5-dimercapto-1,3,4-thiadiazole are dissolved in 240 cm. of 80% aqueous ethanol containing 8 g. (0.2 mol) of sodium hydroxide. After adding 17.5 g. (0.1 mol) of 1,4-bis-chloromethylbenzol the reaction mixture is refluxed for 2 hours and cooled. The precipitate is filtered by suction and washed with water until free from halogen. The raw material is dissolved in dimethylformamide and reprecipitated by adding water.

Yield: 18 g. Melting point: 223.

The compounds having the general Formula III may be prepared by the method described by Hiroshi Kato and Masaki Ohta in the Journal of the Chemical Society of Japan, Pure Chemistry Section [Nippon Kagaku Zassi], vol. 78, pages 1588-91 (November 1957), abstracts of which appear in Chemical Abstracts, vol. 54, column 1502b (1960) and in Chemisches Zentralbla-tt, 1958 volume, page 13,775 according to the following example:

COMPOUND 42 To a suspension of 12.4 g. of succinic acid dihydrazide (NH NHCOCH CH CONHNH in a solution of 10 g. potassium hydroxide in 200 cm. methanol are added dropwise with stirring 20 g. carbon disulphide diluted with cm? methanol. The resulting hydroscopic potassium salt is mixed with 300 g. concentrated sulphuric acid while the reaction mixture is cooled with ice. After one hour the solution is stirred into ice. The crude pre cipitated product is dissolved in dilute aqueous sodium hydroxide and reprecipitated with hydrochloric acid.

By adding one of the compounds mentioned above to a solution of a developer the darkening is retarded for a considerable period and the formation of a black mud is prevented. Thus the deleterious effect on the photographic material is avoided. Of particular importance is the advantageous effect on developer solutions used for the silver salt diffusion process, which solutions contain a certain quantity of solvent for silver halide, generally sodium thiosulphate.

The quantity of mercaptothiadiazole which has to be added depends on the composition of the developer and the effect desired, and varies between 10 and 100 mg. per litre ofdeveloper solution.

Example 1 A developer containing per litre of water:

100 g. dry sodium 'sulphite 12 g. hydroquinone 9 g. sodium hydroxide 1 g. 1-phenylpyrazolidone-3 and 1.5 g. potassium bromide is dark after 60* silver salt diffusion copies had passed through it, and has a black deposit. If 0.1 g./1. of substance 42 is added to the same developer, the developer remains pale yellow in colour and free from dark deposit.

Example 2 20-40 mg. of substance 10 are added to a developer as in Example 1. After 100 copies have been made, this developer is still pale in colour. No muddy deposits have been observed. i

Example 3 If 35 mg. of substance 21 are added to a developer as in Example 1, there is no darkening of colour even after 100 copies have been made.

Example 4 80 mg. of substance 32 are added to the same developer as in Example 1. Even after 100 copies had been made, the developer solution remains considerably paler than a developer without the additive which was used accordingly.

Example 5 A developer containing per litre of water:

100 g. dry sodium sulphite 12 gfhydroquinone 4 g. N-methyl-p-aminophenol sulfate (Metol developer) 9 g. sodium hydroxide and 2 g. potassium bromide is coloured black-brown after 100 silver salt diffusion copies have been processed and has a deposit of the same colour which produces stains on the copies.

A developer of the same constitution but containing 80 mg./l. of substance 31 remains pale yellow in colour after the same number of copies have passed through it. No precipitate has been observed.

Example 6 4O mg./1. of substance 34 are added to the developer as in Example 3. The developer is still pale after 100 copies have been made.

Example 7 50 mg. of substance 3 are added to the developer as in Example 3. After 75 copies have been made, the developer is still pale yellow in colour and produces no stains on the copies.

Example 8 20-30 mg. of substance 12 are added to a developer as in Example 3. After 75-100 copies have been made, no formation of deposit is observed. A developer of the same constitution but Without the additive is after 75 copies have been processed already darkened and contains a muddy precipitate.

Example 9 A developer containing per litre of water:

45 g. sodium carbonate 60 g. sodium sulphite 1.5 g. N-methyl-p-aminophenol sulfate (Metol developer) 6 g. hydroquinone and 1 g. KBr, shows a yellow-brown colour after it has been used for processing 2.5 m? silver chloride paper.

If 70 mg. of compound 38 are added per litre of developer, the used developer solution remains unchanged even after it has been left to stand for some time.

The foregoing examples were selected to illustrate the present invention, it being understood that these examples represent preferred embodiments but are not to be considered as limiting the invention thereto. The remainder of the developer composition are not critical and are selected according to the requirements of the particular reproduction process for which the developer composition is to be used. For example as developer compounds may be utilized hydroquinone, p-methylaminophenol, 1-phenyl-3-pyrazolidone, 1-p-aminophenyl-3-amino-pyraz 'olone, phenylendiamine derivatives and the like. The developer may contain antioxidants such as alkali-metal sulphites, bisulphites, metasulfites or metahydrogen sulphites or any conventional stabilizing agent. The developer composition can be alkalized with alkali-metal hydroxides, phosphates, borates, carbonates and the like.

The developer com-positions according to the invention may be used for processing of any kind of photographic material. Although the compounds according to the invention are preferably added to developer compositions that are intended to be used in the silver salt diifusion process said compounds can also be employed in compositions for developing black and white or color photographic materials.

We claim:

1. In the silver salt difiusion process for developing an exposed silver halide emulsion layer in an aqueous alkaline photographic developer composition the improvement comprising preventing the darkening and formation of precipitates in the developer composition by the addition thereto of an effective amount of a 2-mercapto-1,3,4 thiadiazole derivative Whose formula is selected from the group consisting of and (III) in which X is a bivalent radical of the group consisting of thio and imino,

R is a radical of the group consisting of alkyl containing from 3 to 16 carbon atoms, cycloalkyl, phenyl, phenylalkyl, and halogen-substituted, alkoxy-substituted, lower-ailkyl-substituted, cycloalkyl-substituted, and phenyl-substituted cycloalkyl, phenyl, phenylalkyl, and alkyl radicals containing from 3 to 16 carbon atoms,

R is a radical of the group consisting of alkylene containing from 4 to 10 carbon atoms, cycloalkylene, phenylene, phenylalkylene, and halogen-substituted, alkoxy-substit-uted and lower-alkyl-substituted cycloalkylene, phenylene, phenylalkylene and alkylene radicals containing from 4 to 10 carbon atoms, and

n is an integer from 0 to 6.

2. The combination as defined in claim 1 in which the developer composition contains a silver halide solvent selected from the group consisting of sodium thiosulphate, potassium thiosulphate, calcium thiosulphate and ammonium thiosulphate.

3. The combination as defined in claim 1 in which the derivative of 2-mercapto-1,3,4 thi-adiazole is added in an amount equivalent to between 10 and milligrams per liter of aqueous photographic developing composition.

4. The combination according to claim 1 wherein the 2-mercapto-1,3,4 thiadiazole derivative has the following formula 5. In a silver salt diffusion photographic developing composition containing an effective amount of a developer and a silver halide solvent the improvement according to which the composition contains a 2-mercapto 1,3,4 thiadiazole derivative whose formula is selected from the group consisting of and (III) in which X is a bivalent radical of the group consisting of thio and imino,

R is a radical of the group consisting of alkyl containing from 3 to 16 carbon atoms, cycloalkyl, phenyl, phenylalkyl, and halogen-substituted, aikoxy-su-bstituted, lower-alkyl-substituted, cycloalkyl-substituted, and phenyl-su-bstituted cycloalkyl, phenyl, phenylalkyl, and alkyl radicals containing from 3 to 16 carbon atoms,

R is a radical of the group consisting of alkylene containing from 4 to 10 carbon atoms, cycloalkylene, phenylene, phenylalkylene, and halogen-substituted, alkoxy-substituted and lower-alkyl-substituted cycloalkylene, phenylene, phenylalkylene and alkylene radicals containing from 4 to 10 carbon atoms, and

n is an integer from to 6, in an amount sufficient to prevent darkening and the formation of precipitates in the composition.

6. The combination according to claim 5 wherein the 2-mercapto1,3,4 thiadiazole derivative has the following formula References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS Germany.

OTHER REFERENCES Chemical Abstracts, vol. 54, page 1502 (1960).

NORMAN G. TORCHIN, Primary Examiner. 

1. IN THE SILVER SALT DIFFUSION PROCESS FOR DEVELOPING AN EXPOSED SILVER HALIDE EMULSION LAYER IN AN AQUEOUS ALKALINE PHOTOGRAPHIC DEVELOPER COMPOSITION THE IMPROVEMENT COMPRISING PREVENTING THE DARKENING AND FORMATION OF PRECIPITATES IN THE DEVELOPER COMPOSITION BY THE ADDITION THERETO OF AN EFFECTIVE AMOUNT OF A 2-MERCAPTO-1,3,4 THIADIAZOLE DERIVATIVE WHOSE FORMULA IS SELECTED FROM THE GROUP CONSISTING OF 